Pump

ABSTRACT

The invention relates to a pump having a pump casing, in which a pump chamber is formed, having an inlet leading to it and an outlet leading away from it. In the pump chamber there is a pump impeller, which is secured to a drive shaft, which can be driven in rotation and is mounted rotatably in bearings in the pump casing. Surfaces of the pump chamber which bear against the surfaces of the pump impeller and surfaces of the pump impeller which bear against the surfaces of the pump chamber have a coating of low thickness and high hardness which is applied by physical vapor deposition.

CLAIM FOR PRIORITY

[0001] This application claims priority to Application No. 10201405.1which was filed in the German language on Jan. 15, 2002.

TECHNICAL FIELD OF THE INVENTION

[0002] The invention relates to a pump, and in particular, to a fuelpump.

BACKGROUND OF THE INVENTION

[0003] For pumps which deliver aggressive liquids, such as fuels, it isknown to provide the inner parts of the pumps with a layer of anodizedmetal to protect against corrosion.

[0004] Currently, fuels increasingly include contaminants, which lead towear between the parts of the pumps which move relative to one anotherand damage the layer of anodized metal. Fuels contaminated by water orsubstances which undergo similar chemical reactions and a very widerange of additives in the fuels can then lead to further damage to thepump parts.

[0005] In the case of pump components made from aluminum, fuels with ahigh alcohol content lead to oxidation and therefore to blooming andultimately to the pump impeller becoming blocked. A blockage of thistype may also result from the contamination.

[0006] However, very small gaps are required between the moving andstationary pump parts, so that it is possible to build up sufficientpressure, in particular, in the case of a pump which is constructed as aflow pump.

[0007] Further drawbacks of the layer of anodized metal are the highcost of this layer, its environmental incompatibility and itsconsiderable thickness of approximately 30 μm, which leads to widetolerances. These wide tolerances in turn do not allow a satisfactorybuild-up of pressure in the pump.

[0008] To mount and guide the drive shaft, bearings, for example in theform of carbon bushes, are arranged in bearing bores in the pump casing.This involves a high level of outlay in terms of assembly andcomponents.

SUMMARY OF THE INVENTION

[0009] The invention relates to a pump, in particular a fuel pump,having a pump casing, in which a pump chamber is formed, which has aninlet leading to it and an outlet leading away from it, having a pumpimpeller which is arranged in the pump chamber and is secured to a driveshaft, which can be driven in rotation and is mounted rotatably inbearings in the pump casing.

[0010] The invention provides a pump of the type described in theintroduction which is of simple structure and low-wear design andpermanently ensures a high build-up of pressure.

[0011] According to one embodiment of the invention, surfaces of thepump chamber which bear against surfaces of the pump impeller and/orsurfaces of the pump impeller which bear against surfaces of the pumpchamber have a coating of low thickness and high hardness which isapplied by physical vapor deposition.

[0012] The thin coating can be applied with an exactly uniform thicknessand thereby makes it possible to maintain low tolerances, so that a goodbuild-up of pressure in the pump is ensured.

[0013] The fact that the coating is built up with a uniform layer growthof dense structure and smooth surface also contributes to this, andfurthermore leads to good protection against corrosion and allows thepump to be used for a very wide range of fuel grades and other deliverymedia.

[0014] The high hardness protects the coating from wear and ensures thatthe pump has a long service life. This hardness may preferably lie in arange from 2500 HV to 3500 HV (Vickers hardness), but may also lie aboveor below this range.

[0015] Since low process temperatures are required to produce thecoating, there is no distortion of the coated components or changes inthe material, for example the microstructure, at these components.

[0016] Since, furthermore, the coating can be applied to a very widerange of materials, it is in each case possible to use the optimummaterials and material pairings for pump casing and pump impeller.

[0017] The layer is applied in a manner which does not pollute theenvironment.

[0018] In another embodiment, the drive shaft is mounted rotatably inbearing bores in the pump casing, the bearing bores and/or the driveshaft having a coating of low thickness and high hardness which isapplied by physical vapor deposition.

[0019] In addition to the features of pump casing and pump impeller, thevery hard and smooth surface of the coating of bearing bore and/or driveshaft and the tight tolerances means that these parts will transfer thepositive properties of a carbon bush as a bearing directly to the simplebearing bore. In this way, it is possible to eliminate separate bearingsand the machining of these bearings. If the pump is a flow pump, thetight tolerances of the components which are inevitably required in flowpumps in order to build up pressure and therefore the small gaps betweenthe components which move relative to one another can be minimized.

[0020] This is advantageous in particular if the flow pump is aperipheral impeller or side channel pump.

[0021] Over and above those surfaces of pump impeller and pump chamberwhich bear against one another, it is also possible for the entiresurface of the pump chamber to be provided with a coating which isapplied by physical vapor deposition, with the surfaces of thefuel-carrying parts of the pump preferably also being provided with acoating which is applied by physical vapor deposition. As a result, itis possible for the pump to deliver even aggressive media without anydamage.

[0022] The fact that the coating has a thickness of approximately 2 μmto approximately 5 μm makes it possible to ensure that the tightproduction tolerances are met. A layer thickness of 2 μm is entirelysufficient to protect against wear, while 5 μm is preferred if the layeris to protect against corrosion.

[0023] Particularly when the pump is used as a fuel pump, the coating ispreferably a chromium nitride layer.

[0024] The pump casing and/or pump impeller may include metal or a metalalloy, in particular of aluminum or aluminum alloy, which are madewear-resistant and corrosion-resistant by the coating but are still easyto produce and lightweight.

[0025] In one alternative, the pump casing and/or pump impeller includesa plastic, in particular a phenolic resin. Parts of this type, which caneasily be produced as injection moldings and have a low weight, are alsomade wear-resistant and able to withstand aggressive delivery media bythe coating.

[0026] A particularly favorable material pairing consists in the pumpcasing including coated aluminum and the pump impeller includingphenolic resin. The pump impeller consisting of phenolic resin may becoated or uncoated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] An exemplary embodiment of the invention is illustrated in thedrawing and is described in more detail below.

[0028]FIG. 1 shows a fuel pump with flow pumps as pump stages.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The pump illustrated in FIG. 1 is a two-stage fuel pump. Anelectric motor arranged in the closed motor casing 1 illustrated can beused to drive a drive shaft 2 in rotation, a first pump impeller 3 of aperipheral impeller pump 14 being arranged in a rotationally fixedmanner on the right-hand end region of this drive shaft 2. The radiallyencircling region of the first pump impeller 3 is formed with a firstring of vanes, which is largely surrounded by an annular passage. Afirst pump chamber 5 is formed as a pot-shaped recess 31 in one end sideof a cover 6 which is part of the pump casing 7.

[0030] In the pump cover 7 there is an inlet 8, via which the peripheralimpeller pump can suck in fuel. Furthermore, a ball 9 is arrangedcentrally in a receptacle on the side of the first pump impeller 3 inthe cover 6, against which ball the drive shaft 2 is supported at theend side and which ball forms an axial bearing of the drive shaft 2.

[0031] The first pump chamber 5 is closed off by a partition 10 whichbears against the opening in the pot-shaped recess 31 in the cover 6 andthrough which the drive shaft is guided. The drive shaft 2 is guidedthrough a bearing bore 11 in the partition 10, which likewise forms apart of the pump casing 7, and is rotatably mounted directly in thisbearing bore 11.

[0032] In a plane which cannot be seen, the first pump chamber 5 isconnected to a radially encircling annular passage 12 on that side inthe partition 10 which faces the peripheral impeller pump 14, aconnection 13 leading from this annular passage 12 to that side of thepartition 10 which is remote from the peripheral impeller pump 14 andopening out into a first side passage 15, which is formed in the shapeof a ring at that location, of a side channel pump 16.

[0033] On the side of the first side channel 15, the partition 10 islikewise designed with a pot-shaped recess 17, which forms a second pumpchamber and in which a second pump impeller 18 of the side channel pump16 is arranged, this second pump impeller likewise being seated in arotationally fixed manner on the drive shaft 2.

[0034] In one of its side faces, the second pump impeller 18 has asecond ring of vanes 19 which is aligned with the first side channel 16and is connected, via axial apertures 20, to a third ring of vanes 21 onthe other side face of the pump impeller 18.

[0035] The third ring of vanes 21 is covered by an annular second sidechannel 22, which is formed in a partition 23, closes off the pot-shapedopening 14, forms part of the pump casing 7 and is guided through adrive shaft 2.

[0036] The partition 23 separates the side channel pump 16 from themotor casing 1, the outlet 24 formed in the partition 23 opening outinto the motor casing 1. The fuel which is delivered flows through themotor casing 1 and is fed via a nonreturn valve 25 to a pressure port 26of the fuel pump, which are arranged in a closure wall 29. A plugcontact 30 for supplying power to the electric motor is likewise locatedin the closure wall 29.

[0037] A bearing wall 27, which has a second bearing bore 28 coaxiallywith respect to the first bearing bore 11, is arranged in the end regionof the motor casing 1 on the side of the pressure port 27, in whichsecond bearing bore 28 the left-hand end of the drive shaft 2 isdirectly rotatably mounted.

[0038] The two pump impellers 3 and 18 comprise phenolic resin. Theparts of the pump casing 7 are formed from aluminum. In all the regionswhich face the partition 10 and in the inlet 8, the cover 6 has acoating of chromium nitride. The partition 10, the separating wall 23and the bearing wall 27 are completely provided with a coating ofchromium nitride. Furthermore, the surfaces of the closure wall 29 andof the pressure port 26 around which the fuel washes are coated withchromium nitride.

[0039] The cylindrical inner walls of the first and second bearing bores11 and 28 are also coated. In addition, the drive shaft 2 consisting ofsteel has a chromium nitride coating in its regions located in thebearing bores 11 and 28.

[0040] These chromium nitride coatings have been applied by physicalvapor deposition and have a thickness of 5 μm and a Vickers Hardness ofapproximately 2500 HV.

LIST OF REFERENCE SYMBOLS FOR DRAWING FIGURE

[0041]1 Motor casing

[0042]2 Drive shaft

[0043]3 First pump impeller

[0044]4 Ring of vanes

[0045]5 First pump chamber

[0046]6 Cover

[0047]7 Pump casing

[0048]8 Inlet

[0049]9 Ball

[0050]10 Partition

[0051]11 First bearing bore

[0052]12 Annular passage

[0053]13 Connection

[0054]14 Peripheral impeller pump

[0055]15 First side channel

[0056]16 Side channel pump

[0057]17 Pot-shaped recess

[0058]18 Second pump impeller

[0059]19 Second ring of vanes

[0060]20 Axial apertures

[0061]21 Third ring of vanes

[0062]22 Second side channel

[0063]23 Separating wall

[0064]24 Outlet

[0065]25 Nonreturn valve

[0066]26 Pressure port

[0067]27 Bearing wall

[0068]28 Second bearing bore

[0069]29 Closure wall

[0070]30 Plug contact

[0071]31 Pot-shaped recess

What is claimed is:
 1. A pump, comprising: a pump casing, in which apump chamber is formed, which has an inlet leading to the casing and anoutlet leading away from the casing; and a pump impeller which isarranged in the pump chamber and is secured to a drive shaft, which canbe driven in rotation and is mounted rotatably in bearings in the pumpcasing, wherein surfaces of the pump chamber which bear against surfacesof the pump impeller and/or surfaces of the pump impeller which bearagainst surfaces of the pump chamber have a coating of low thickness andhigh hardness which is applied by physical vapor deposition.
 2. The pumpaccording to claim 1, wherein the drive shaft is mounted rotatably inbearing bores in the pump casing, the bearing bores and/or the driveshaft having a coating of low thickness and high hardness which isapplied by physical vapor deposition.
 3. The pump according to claim 1,wherein the pump is a flow pump.
 4. The pump according to claim 3,wherein the flow pump is a peripheral impeller or side channel pump. 5.The pump according to claim 1, wherein the surface of the pump chamberis provided with a coating which is applied by physical vapordeposition.
 6. The pump according to claim 1, wherein the surfaces ofthe fuel-carrying parts of the pump are provided with a coating which isapplied by physical vapor deposition.
 7. The pump according to claim 1,wherein the coating has a thickness of approximately 2 μm toapproximately 5 μm.
 8. The pump according to claim 1, wherein thecoating is a chromium nitride layer.
 9. The pump according to claim 1,wherein the pump casing and/or pump impeller comprises metal or a metalalloy.
 10. The pump according to claim 1, wherein the pump casing and/orpump impeller comprises a plastic.
 11. The pump according to claim 1,wherein the pump is a fuel pump.